Knee Biomechanics

what kind of joint is the knee joint?

synovial, diarthroses, condyloid

7 key features of all synovial joints

1. synovial fluid

2. articular capsule

3. articular cartilage

4. synovial membrane

5. capsular ligaments

6. blood vessels

7. sensory nerves

extra features of synovial joints

• intraarticular discs/menisci

• fat pads

• labrum

• synovial plicae

• bursa

in the knee, the axis of rotation moves based on

the orientation of the femur and tibia relative to one another

evolute

the path of motion of the instantaneous axis of rotation

the evolute is longer when

the joint surfaces are less congruent

shaft of the femur is slanted

medially from the hip

normal lateral angle of the knee joint

170-175

the knee is naturally in slight genu

valgum

<170 degree lateral angle

excessive genu valgum

>180 degree lateral knee angle

excessive genu varum

with a valgus force, what ligament is at risk

MCL

with a varus force, what ligament is at risk

LCL

knee flexors

• biceps femoris

• semitendinosus

• semimembranosus

• gracilis

• sartorious

• popliteus

• gastrocnemius

knee extensors

• rectus femoris

• vastus medialis

• vastus lateralis

• vastus intermedius

medial rotators of the knee

• popliteus

• gracilis

• semitendinosus

• semimembranosus

• sartorious

lateral rotators of the knee

biceps femoris

fat pads of the knee

supra and infrapatellar

which femoral condyle is longer/has larger surface

medial

cruciate ligaments attach to the

intercondylar fossa/notch

posterior tibial slope

angle of the tibia from anterior to posterior

increased posterior tibial slope, increased risk of

ACL tear

the knee has the most IR/ER at

90 degrees flexion

close-pack position of the knee

full extension (least motion available)

what muscle helps to unlock the knee

popliteus

tibial adduction

genu varus

tibial abduction

knee valgus

medial and lateral collateral ligaments

• resist excessive frontal plane movement

• generalized stabilization in extended knee

• resist A-P shear forces between tibia and femur

cruciate ligaments are named for their attachment on

the tibia

two bundles of the ACL

anterior-medial

posterior-lateral

ACL becomes more taut as knee moves into

extension

two bundles of the PCL

anterior-lateral

anterior-medial

PCL gets more taut as knee moves into

extension

common PCL tear injury

dashboard injury

patellofemoral joint

articular side of patella and trochlear groove of femur

local stabilizers of patella

• quadriceps force

• bony congruence of articular surfaces

• passive restraint of soft tissues

patella moves with the

patellar tendon and quad muscle/tendon

patella shifts ___ with extension and ____ with flexion

inferior; superior

patella is most stable when in

trochlear groove - flexion

patella function

increase the moment arm of the quadriceps

torque =

force x moment arm

in full flexion, the moment arm of the quadriceps is

least????? slide 55

knee flexion in a closed chain puts ____ compressive force on the patella

more

knee flexion ____ compressive forces in a closed chain due to

increases; change in angle of patella tendon and quads

when working with a patient with knee OA doing closed chain exercise:

squats —> AVOID terminal flexion

knee extension ____ compressive forces in an open chain

increases

when working with a patient with knee OA doing open chain exercise:

leg press —> AVOID full extension

in genu valgum, compressive forces are on the ___ side

lateral

in genu varum, compressive forces are on the ___ side

medial

genu recurvatum

excessive knee extension - more force on the anterior side

medial meniscus

c-shaped

tight, securely attached to tibia

strong attachments to medial joint capsule, MCL, ACL, semimembranosus

lateral meniscus

o-shaped

more mobile than medial

loose attachment to lateral joint capsule, PCL, popliteus

functions of the menisci

1. stabilize by deepening the socket

2. reduce compressive stress by absorbing shock from WB/loading stress

3. lubricate joint

4. increase congruency, weight distribution, increase contact area

5. posterior wedge —> secondary restraint to anterior tibial translation

menisci move with the

tibia during flexion and extension

menisci move ___ during flexion due to

posterior; semi-membranous and popliteus muscle pull

menisci move ___ during extension due to

anterior; pull of coronary ligaments

red-red zone

outer 1/3 of meniscus

red-white zone

middle 1/3 of meniscus

white-white zone

inner 1/3 of of meniscus